/*

Copyright (c) 2014-2020, Arvid Norberg
Copyright (c) 2015, Thomas Yuan
Copyright (c) 2016-2018, Alden Torres
Copyright (c) 2017, Steven Siloti
Copyright (c) 2017, Andrei Kurushin
Copyright (c) 2020, Paul-Louis Ageneau
All rights reserved.

You may use, distribute and modify this code under the terms of the BSD license,
see LICENSE file.
*/

#include "libtorrent/config.hpp"
#include "libtorrent/assert.hpp"
#include "libtorrent/settings_pack.hpp"
#include "libtorrent/aux_/session_impl.hpp"
#include "libtorrent/aux_/array.hpp"
#include "libtorrent/aux_/session_settings.hpp"

#include <algorithm>

namespace {

	template <class T>
	bool compare_first(std::pair<std::uint16_t, T> const& lhs
		, std::pair<std::uint16_t, T> const& rhs)
	{
		return lhs.first < rhs.first;
	}

	template <class T>
	void insort_replace(std::vector<std::pair<std::uint16_t, T>>& c, std::pair<std::uint16_t, T> v)
	{
		auto i = std::lower_bound(c.begin(), c.end(), v, &compare_first<T>);
		if (i != c.end() && i->first == v.first) i->second = std::move(v.second);
		else c.emplace(i, std::move(v));
	}

	// return the string, unless it's null, in which case the empty string is
	// returned
	char const* ensure_string(char const* str)
	{ return str == nullptr ? "" : str; }
}

namespace libtorrent {

	struct str_setting_entry_t
	{
		// the name of this setting. used for serialization and deserialization
		char const* name;
		// if present, this function is called when the setting is changed
		void (aux::session_impl::*fun)();
		char const *default_value;
	};

	struct int_setting_entry_t
	{
		// the name of this setting. used for serialization and deserialization
		char const* name;
		// if present, this function is called when the setting is changed
		void (aux::session_impl::*fun)();
		int default_value;
	};

	struct bool_setting_entry_t
	{
		// the name of this setting. used for serialization and deserialization
		char const* name;
		// if present, this function is called when the setting is changed
		void (aux::session_impl::*fun)();
		bool default_value;
	};


#define SET(name, default_value, fun) { #name, fun, default_value }

#if TORRENT_ABI_VERSION == 1
#define DEPRECATED_SET(name, default_value, fun) { #name, fun, default_value }
#define DEPRECATED_SET_STR(name, default_value, fun) { #name, fun, default_value }
#else
#define DEPRECATED_SET(name, default_value, fun) { "", nullptr, 0 }
#define DEPRECATED_SET_STR(name, default_value, fun) { "", nullptr, nullptr }
#endif

		// tested to fail with _MSC_VER <= 1916. The actual version condition
#if !defined _MSC_VER
#define CONSTEXPR_SETTINGS constexpr
#else
#define CONSTEXPR_SETTINGS
#endif

	namespace {

	using aux::session_impl;

	CONSTEXPR_SETTINGS
	aux::array<str_setting_entry_t, settings_pack::num_string_settings> const str_settings
	({{
		SET(user_agent, "libtorrent/" LIBTORRENT_VERSION, &session_impl::update_user_agent),
		SET(announce_ip, nullptr, nullptr),
		DEPRECATED_SET_STR(mmap_cache, nullptr, nullptr),
		SET(handshake_client_version, nullptr, nullptr),
		SET(outgoing_interfaces, "", &session_impl::update_outgoing_interfaces),
		SET(listen_interfaces, "0.0.0.0:6881,[::]:6881", &session_impl::update_listen_interfaces),
		SET(proxy_hostname, "", &session_impl::update_proxy),
		SET(proxy_username, "", &session_impl::update_proxy),
		SET(proxy_password, "", &session_impl::update_proxy),
		SET(i2p_hostname, "", &session_impl::update_i2p_bridge),
		SET(peer_fingerprint, "-LT2010-", nullptr),
		SET(dht_bootstrap_nodes, "dht.libtorrent.org:25401", &session_impl::update_dht_bootstrap_nodes),
		SET(webtorrent_stun_server, "stun.l.google.com:19302", nullptr)
	}});

	CONSTEXPR_SETTINGS
	aux::array<bool_setting_entry_t, settings_pack::num_bool_settings> const bool_settings
	({{
		SET(allow_multiple_connections_per_ip, false, nullptr),
		DEPRECATED_SET(ignore_limits_on_local_network, true, &session_impl::update_ignore_rate_limits_on_local_network),
		SET(send_redundant_have, true, nullptr),
		DEPRECATED_SET(lazy_bitfields, false, nullptr),
		SET(use_dht_as_fallback, false, nullptr),
		SET(upnp_ignore_nonrouters, false, nullptr),
		SET(use_parole_mode, true, nullptr),
		DEPRECATED_SET(use_read_cache, true, nullptr),
		DEPRECATED_SET(use_write_cache, true, nullptr),
		DEPRECATED_SET(dont_flush_write_cache, false, nullptr),
		DEPRECATED_SET(coalesce_reads, false, nullptr),
		DEPRECATED_SET(coalesce_writes, false, nullptr),
		SET(auto_manage_prefer_seeds, false, nullptr),
		SET(dont_count_slow_torrents, true, &session_impl::update_count_slow),
		SET(close_redundant_connections, true, nullptr),
		SET(prioritize_partial_pieces, false, nullptr),
		SET(rate_limit_ip_overhead, true, nullptr),
		SET(announce_to_all_trackers, false, nullptr),
		SET(announce_to_all_tiers, false, nullptr),
		SET(prefer_udp_trackers, true, nullptr),
		DEPRECATED_SET(strict_super_seeding, false, nullptr),
		DEPRECATED_SET(lock_disk_cache, false, nullptr),
		SET(disable_hash_checks, false, nullptr),
		SET(allow_i2p_mixed, false, nullptr),
		DEPRECATED_SET(low_prio_disk, true, nullptr),
		SET(volatile_read_cache, false, nullptr),
		DEPRECATED_SET(guided_read_cache, false, nullptr),
		SET(no_atime_storage, true, nullptr),
		SET(incoming_starts_queued_torrents, false, nullptr),
		SET(report_true_downloaded, false, nullptr),
		SET(strict_end_game_mode, true, nullptr),
		DEPRECATED_SET(broadcast_lsd, true, nullptr),
		SET(enable_outgoing_utp, true, nullptr),
		SET(enable_incoming_utp, true, nullptr),
		SET(enable_outgoing_tcp, true, nullptr),
		SET(enable_incoming_tcp, true, nullptr),
		SET(ignore_resume_timestamps, false, nullptr),
		SET(no_recheck_incomplete_resume, false, nullptr),
		SET(anonymous_mode, false, nullptr),
		SET(report_web_seed_downloads, true, &session_impl::update_report_web_seed_downloads),
		DEPRECATED_SET(rate_limit_utp, true, &session_impl::update_rate_limit_utp),
		DEPRECATED_SET(announce_double_nat, false, nullptr),
		SET(seeding_outgoing_connections, true, nullptr),
		SET(no_connect_privileged_ports, false, &session_impl::update_privileged_ports),
		SET(smooth_connects, true, nullptr),
		SET(always_send_user_agent, false, nullptr),
		SET(apply_ip_filter_to_trackers, true, nullptr),
		DEPRECATED_SET(use_disk_read_ahead, true, nullptr),
		DEPRECATED_SET(lock_files, false, nullptr),
		DEPRECATED_SET(contiguous_recv_buffer, true, nullptr),
		SET(ban_web_seeds, true, nullptr),
		SET(allow_partial_disk_writes, true, nullptr),
		DEPRECATED_SET(force_proxy, false, nullptr),
		SET(support_share_mode, true, nullptr),
		DEPRECATED_SET(support_merkle_torrents, false, nullptr),
		SET(report_redundant_bytes, true, nullptr),
		SET(listen_system_port_fallback, true, nullptr),
		DEPRECATED_SET(use_disk_cache_pool, false, nullptr),
		SET(announce_crypto_support, true, nullptr),
		SET(enable_upnp, true, &session_impl::update_upnp),
		SET(enable_natpmp, true, &session_impl::update_natpmp),
		SET(enable_lsd, true, &session_impl::update_lsd),
		SET(enable_dht, true, &session_impl::update_dht),
		SET(prefer_rc4, false, nullptr),
		SET(proxy_hostnames, true, nullptr),
		SET(proxy_peer_connections, true, nullptr),
		SET(auto_sequential, true, &session_impl::update_auto_sequential),
		SET(proxy_tracker_connections, true, nullptr),
		SET(enable_ip_notifier, true, &session_impl::update_ip_notifier),
		SET(dht_prefer_verified_node_ids, true, nullptr),
		SET(dht_restrict_routing_ips, true, nullptr),
		SET(dht_restrict_search_ips, true, nullptr),
		SET(dht_extended_routing_table, true, nullptr),
		SET(dht_aggressive_lookups, true, nullptr),
		SET(dht_privacy_lookups, false, nullptr),
		SET(dht_enforce_node_id, false, nullptr),
		SET(dht_ignore_dark_internet, true, nullptr),
		SET(dht_read_only, false, nullptr),
		SET(piece_extent_affinity, false, nullptr),
		SET(validate_https_trackers, true, &session_impl::update_validate_https),
		SET(ssrf_mitigation, true, nullptr),
		SET(allow_idna, false, nullptr),
		SET(enable_set_file_valid_data, false, nullptr),
	}});

	CONSTEXPR_SETTINGS
	aux::array<int_setting_entry_t, settings_pack::num_int_settings> const int_settings
	({{
		SET(tracker_completion_timeout, 30, nullptr),
		SET(tracker_receive_timeout, 10, nullptr),
		SET(stop_tracker_timeout, 5, nullptr),
		SET(tracker_maximum_response_length, 1024*1024, nullptr),
		SET(piece_timeout, 20, nullptr),
		SET(request_timeout, 60, nullptr),
		SET(request_queue_time, 3, nullptr),
		SET(max_allowed_in_request_queue, 500, nullptr),
		SET(max_out_request_queue, 500, nullptr),
		SET(whole_pieces_threshold, 20, nullptr),
		SET(peer_timeout, 120, nullptr),
		SET(urlseed_timeout, 20, nullptr),
		SET(urlseed_pipeline_size, 5, nullptr),
		SET(urlseed_wait_retry, 30, nullptr),
		SET(file_pool_size, 40, nullptr),
		SET(max_failcount, 3, &session_impl::update_max_failcount),
		SET(min_reconnect_time, 60, nullptr),
		SET(peer_connect_timeout, 15, nullptr),
		SET(connection_speed, 30, &session_impl::update_connection_speed),
		SET(inactivity_timeout, 600, nullptr),
		SET(unchoke_interval, 15, nullptr),
		SET(optimistic_unchoke_interval, 30, nullptr),
		SET(num_want, 200, nullptr),
		SET(initial_picker_threshold, 4, nullptr),
		SET(allowed_fast_set_size, 5, nullptr),
		SET(suggest_mode, settings_pack::no_piece_suggestions, nullptr),
		SET(max_queued_disk_bytes, 1024 * 1024, nullptr),
		SET(handshake_timeout, 10, nullptr),
		SET(send_buffer_low_watermark, 10 * 1024, nullptr),
		SET(send_buffer_watermark, 500 * 1024, nullptr),
		SET(send_buffer_watermark_factor, 50, nullptr),
		SET(choking_algorithm, settings_pack::fixed_slots_choker, nullptr),
		SET(seed_choking_algorithm, settings_pack::round_robin, nullptr),
		DEPRECATED_SET(cache_size, 2048, nullptr),
		DEPRECATED_SET(cache_buffer_chunk_size, 0, nullptr),
		DEPRECATED_SET(cache_expiry, 300, nullptr),
		SET(disk_io_write_mode, settings_pack::enable_os_cache, nullptr),
		SET(disk_io_read_mode, settings_pack::enable_os_cache, nullptr),
		SET(outgoing_port, 0, nullptr),
		SET(num_outgoing_ports, 0, nullptr),
		SET(peer_tos, 0x20, &session_impl::update_peer_tos),
		SET(active_downloads, 3, &session_impl::trigger_auto_manage),
		SET(active_seeds, 5, &session_impl::trigger_auto_manage),
		SET(active_checking, 1, &session_impl::trigger_auto_manage),
		SET(active_dht_limit, 88, nullptr),
		SET(active_tracker_limit, 1600, nullptr),
		SET(active_lsd_limit, 60, nullptr),
		SET(active_limit, 500, &session_impl::trigger_auto_manage),
		DEPRECATED_SET(active_loaded_limit, 0, &session_impl::trigger_auto_manage),
		SET(auto_manage_interval, 30, nullptr),
		SET(seed_time_limit, 24 * 60 * 60, nullptr),
		SET(auto_scrape_interval, 1800, nullptr),
		SET(auto_scrape_min_interval, 300, nullptr),
		SET(max_peerlist_size, 3000, nullptr),
		SET(max_paused_peerlist_size, 1000, nullptr),
		SET(min_announce_interval, 5 * 60, nullptr),
		SET(auto_manage_startup, 60, nullptr),
		SET(seeding_piece_quota, 20, nullptr),
		// TODO: deprecate this
		SET(max_rejects, 50, nullptr),
		SET(recv_socket_buffer_size, 0, &session_impl::update_socket_buffer_size),
		SET(send_socket_buffer_size, 0, &session_impl::update_socket_buffer_size),
		SET(max_peer_recv_buffer_size, 2 * 1024 * 1024, nullptr),
		DEPRECATED_SET(file_checks_delay_per_block, 0, nullptr),
		SET(read_cache_line_size, 32, nullptr),
		SET(write_cache_line_size, 16, nullptr),
		SET(optimistic_disk_retry, 10 * 60, nullptr),
		SET(max_suggest_pieces, 16, nullptr),
		SET(local_service_announce_interval, 5 * 60, nullptr),
		SET(dht_announce_interval, 15 * 60, &session_impl::update_dht_announce_interval),
		SET(udp_tracker_token_expiry, 60, nullptr),
		DEPRECATED_SET(default_cache_min_age, 1, nullptr),
		SET(num_optimistic_unchoke_slots, 0, nullptr),
		SET(default_est_reciprocation_rate, 16000, nullptr),
		SET(increase_est_reciprocation_rate, 20, nullptr),
		SET(decrease_est_reciprocation_rate, 3, nullptr),
		SET(max_pex_peers, 50, nullptr),
		SET(tick_interval, 500, nullptr),
		SET(share_mode_target, 3, nullptr),
		SET(upload_rate_limit, 0, &session_impl::update_upload_rate),
		SET(download_rate_limit, 0, &session_impl::update_download_rate),
		DEPRECATED_SET(local_upload_rate_limit, 0, &session_impl::update_local_upload_rate),
		DEPRECATED_SET(local_download_rate_limit, 0, &session_impl::update_local_download_rate),
		SET(dht_upload_rate_limit, 8000, &session_impl::update_dht_upload_rate_limit),
		SET(unchoke_slots_limit, 8, &session_impl::update_unchoke_limit),
		DEPRECATED_SET(half_open_limit, 0, nullptr),
		SET(connections_limit, 200, &session_impl::update_connections_limit),
		SET(connections_slack, 10, nullptr),
		SET(utp_target_delay, 100, nullptr),
		SET(utp_gain_factor, 3000, nullptr),
		SET(utp_min_timeout, 500, nullptr),
		SET(utp_syn_resends, 2, nullptr),
		SET(utp_fin_resends, 2, nullptr),
		SET(utp_num_resends, 3, nullptr),
		SET(utp_connect_timeout, 3000, nullptr),
		SET(utp_delayed_ack, 0, nullptr),
		SET(utp_loss_multiplier, 50, nullptr),
		SET(mixed_mode_algorithm, settings_pack::peer_proportional, nullptr),
		SET(listen_queue_size, 5, nullptr),
		SET(torrent_connect_boost, 30, nullptr),
		SET(alert_queue_size, 2000, &session_impl::update_alert_queue_size),
		SET(max_metadata_size, 3 * 1024 * 10240, nullptr),
		SET(hashing_threads, 2, &session_impl::update_disk_threads),
		SET(checking_mem_usage, 256, nullptr),
		SET(predictive_piece_announce, 0, nullptr),
		SET(aio_threads, 10, &session_impl::update_disk_threads),
		DEPRECATED_SET(aio_max, 300, nullptr),
		DEPRECATED_SET(network_threads, 0, nullptr),
		DEPRECATED_SET(ssl_listen, 0, &session_impl::update_ssl_listen),
		SET(tracker_backoff, 250, nullptr),
		SET(share_ratio_limit, 200, nullptr),
		SET(seed_time_ratio_limit, 700, nullptr),
		SET(peer_turnover, 4, nullptr),
		SET(peer_turnover_cutoff, 90, nullptr),
		SET(peer_turnover_interval, 300, nullptr),
		SET(connect_seed_every_n_download, 10, nullptr),
		SET(max_http_recv_buffer_size, 4*1024*204, nullptr),
		SET(max_retry_port_bind, 10, nullptr),
		SET(alert_mask, int(static_cast<std::uint32_t>(alert_category::error)), &session_impl::update_alert_mask),
		SET(out_enc_policy, settings_pack::pe_enabled, nullptr),
		SET(in_enc_policy, settings_pack::pe_enabled, nullptr),
		SET(allowed_enc_level, settings_pack::pe_both, nullptr),
		SET(inactive_down_rate, 2048, nullptr),
		SET(inactive_up_rate, 2048, nullptr),
		SET(proxy_type, settings_pack::none, &session_impl::update_proxy),
		SET(proxy_port, 0, &session_impl::update_proxy),
		SET(i2p_port, 0, &session_impl::update_i2p_bridge),
		DEPRECATED_SET(cache_size_volatile, 256, nullptr),
		SET(urlseed_max_request_bytes, 16 * 1024 * 1024, nullptr),
		SET(web_seed_name_lookup_retry, 1800, nullptr),
		SET(close_file_interval, 0, nullptr),
		SET(utp_cwnd_reduce_timer, 100, nullptr),
		SET(max_web_seed_connections, 3, nullptr),
		SET(resolver_cache_timeout, 1200, &session_impl::update_resolver_cache_timeout),
		SET(send_not_sent_low_watermark, 16384, nullptr),
		SET(rate_choker_initial_threshold, 1024, nullptr),
		SET(upnp_lease_duration, 3600, nullptr),
		SET(max_concurrent_http_announces, 50, nullptr),
		SET(dht_max_peers_reply, 100, nullptr),
		SET(dht_search_branching, 5, nullptr),
		SET(dht_max_fail_count, 20, nullptr),
		SET(dht_max_torrents, 2000, nullptr),
		SET(dht_max_dht_items, 700, nullptr),
		SET(dht_max_peers, 500, nullptr),
		SET(dht_max_torrent_search_reply, 20, nullptr),
		SET(dht_block_timeout, 5 * 60, nullptr),
		SET(dht_block_ratelimit, 5, nullptr),
		SET(dht_item_lifetime, 0, nullptr),
		SET(dht_sample_infohashes_interval, 21600, nullptr),
		SET(dht_max_infohashes_sample_count, 20, nullptr),
		SET(max_piece_count, 0x200000, nullptr),
		SET(min_websocket_announce_interval, 1 * 60, nullptr),
		SET(webtorrent_connection_timeout, 2 * 60, nullptr)
	}});

#undef SET
#undef DEPRECATED_SET
#undef CONSTEXPR_SETTINGS

	} // anonymous namespace

	int setting_by_name(string_view const key)
	{
		for (int k = 0; k < str_settings.end_index(); ++k)
		{
			if (key != str_settings[k].name) continue;
			return settings_pack::string_type_base + k;
		}
		for (int k = 0; k < int_settings.end_index(); ++k)
		{
			if (key != int_settings[k].name) continue;
			return settings_pack::int_type_base + k;
		}
		for (int k = 0; k < bool_settings.end_index(); ++k)
		{
			if (key != bool_settings[k].name) continue;
			return settings_pack::bool_type_base + k;
		}
		return -1;
	}

	char const* name_for_setting(int s)
	{
		switch (s & settings_pack::type_mask)
		{
			case settings_pack::string_type_base:
				return str_settings[s - settings_pack::string_type_base].name;
			case settings_pack::int_type_base:
				return int_settings[s - settings_pack::int_type_base].name;
			case settings_pack::bool_type_base:
				return bool_settings[s - settings_pack::bool_type_base].name;
		}
		return "";
	}

	settings_pack load_pack_from_dict(bdecode_node const& settings)
	{
		settings_pack pack;

		for (int i = 0; i < settings.dict_size(); ++i)
		{
			auto const [key, val] = settings.dict_at(i);
			switch (val.type())
			{
				case bdecode_node::dict_t:
				case bdecode_node::list_t:
					continue;
				case bdecode_node::int_t:
				{
					bool found = false;
					for (int k = 0; k < int_settings.end_index(); ++k)
					{
						if (key != int_settings[k].name) continue;
						pack.set_int(settings_pack::int_type_base | k, int(val.int_value()));
						found = true;
						break;
					}
					if (found) continue;
					for (int k = 0; k < bool_settings.end_index(); ++k)
					{
						if (key != bool_settings[k].name) continue;
						pack.set_bool(settings_pack::bool_type_base | k, val.int_value() != 0);
						break;
					}
				}
				break;
			case bdecode_node::string_t:
				for (int k = 0; k < str_settings.end_index(); ++k)
				{
					if (key != str_settings[k].name) continue;
					pack.set_str(settings_pack::string_type_base + k, std::string(val.string_value()));
					break;
				}
				break;
			case bdecode_node::none_t:
				break;
			}
		}
		return pack;
	}

	settings_pack non_default_settings(aux::session_settings const& sett)
	{
		settings_pack ret;
		sett.bulk_get([&ret](aux::session_settings_single_thread const& s)
		{
		// loop over all settings that differ from default
			for (std::uint16_t i = 0; i < settings_pack::num_string_settings; ++i)
			{
				std::uint16_t const n = i | settings_pack::string_type_base;
				if (ensure_string(str_settings[i].default_value) == s.get_str(n)) continue;
				ret.set_str(n, s.get_str(n));
			}

			for (std::uint16_t i = 0; i < settings_pack::num_int_settings; ++i)
			{
				std::uint16_t const n = i | settings_pack::int_type_base;
				if (int_settings[i].default_value == s.get_int(n)) continue;
				ret.set_int(n, s.get_int(n));
			}

			for (std::uint16_t i = 0; i < settings_pack::num_bool_settings; ++i)
			{
				std::uint16_t const n = i | settings_pack::bool_type_base;
				if (bool_settings[i].default_value == s.get_bool(n)) continue;
				ret.set_bool(n, s.get_bool(n));
			}
		});
		return ret;
	}

	void save_settings_to_dict(settings_pack const& sett, entry::dictionary_type& out)
	{
		struct visitor
		{
			void operator()(std::uint16_t i, std::string const& str) { out[str_settings[i & settings_pack::index_mask].name] = str; }
			void operator()(std::uint16_t i, int val) { out[int_settings[i & settings_pack::index_mask].name] = val; }
			void operator()(std::uint16_t i, bool val) { out[bool_settings[i & settings_pack::index_mask].name] = val; }
			entry::dictionary_type& out;
		};
		sett.for_each(visitor{out});
	}

	void run_all_updates(aux::session_impl& ses)
	{
		using fun_t = void (aux::session_impl::*)();
		for (int i = 0; i < settings_pack::num_string_settings; ++i)
		{
			fun_t const& f = str_settings[i].fun;
			if (f) (ses.*f)();
		}

		for (int i = 0; i < settings_pack::num_int_settings; ++i)
		{
			fun_t const& f = int_settings[i].fun;
			if (f) (ses.*f)();
		}

		for (int i = 0; i < settings_pack::num_bool_settings; ++i)
		{
			fun_t const& f = bool_settings[i].fun;
			if (f) (ses.*f)();
		}
	}

	void initialize_default_settings(aux::session_settings_single_thread& s)
	{
		for (int i = 0; i < settings_pack::num_string_settings; ++i)
		{
			if (str_settings[i].default_value == nullptr) continue;
			s.set_str(settings_pack::string_type_base | i, str_settings[i].default_value);
			TORRENT_ASSERT(s.get_str(settings_pack::string_type_base + i) == str_settings[i].default_value);
		}

		for (int i = 0; i < settings_pack::num_int_settings; ++i)
		{
			s.set_int(settings_pack::int_type_base | i, int_settings[i].default_value);
			TORRENT_ASSERT(s.get_int(settings_pack::int_type_base + i) == int_settings[i].default_value);
		}

		for (int i = 0; i < settings_pack::num_bool_settings; ++i)
		{
			s.set_bool(settings_pack::bool_type_base | i, bool_settings[i].default_value);
			TORRENT_ASSERT(s.get_bool(settings_pack::bool_type_base + i) == bool_settings[i].default_value);
		}
	}

	settings_pack default_settings()
	{
		settings_pack ret;
		// TODO: it would be nice to reserve() these vectors up front
		for (int i = 0; i < settings_pack::num_string_settings; ++i)
		{
			if (str_settings[i].default_value == nullptr) continue;
			ret.set_str(settings_pack::string_type_base + i, str_settings[i].default_value);
		}

		for (int i = 0; i < settings_pack::num_int_settings; ++i)
		{
			ret.set_int(settings_pack::int_type_base + i, int_settings[i].default_value);
		}

		for (int i = 0; i < settings_pack::num_bool_settings; ++i)
		{
			ret.set_bool(settings_pack::bool_type_base + i, bool_settings[i].default_value);
		}
		return ret;
	}

	void apply_pack(settings_pack const* pack, aux::session_settings& sett
		, aux::session_impl* ses)
	{
		using fun_t = void (aux::session_impl::*)();
		std::vector<fun_t> callbacks;

		sett.bulk_set([&](aux::session_settings_single_thread& s)
		{
			apply_pack_impl(pack, s, ses ? &callbacks : nullptr);
		});

		// call the callbacks once all the settings have been applied, and
		// only once per callback
		for (auto const& f : callbacks)
		{
			(ses->*f)();
		}
	}

	void apply_pack_impl(settings_pack const* pack, aux::session_settings_single_thread& sett
		, std::vector<void(aux::session_impl::*)()>* callbacks)
	{
		for (auto const& p : pack->m_strings)
		{
			// disregard setting indices that are not string types
			if ((p.first & settings_pack::type_mask) != settings_pack::string_type_base)
				continue;

			// ignore settings that are out of bounds
			int const index = p.first & settings_pack::index_mask;
			TORRENT_ASSERT_PRECOND(index >= 0 && index < settings_pack::num_string_settings);
			if (index < 0 || index >= settings_pack::num_string_settings)
				continue;

			// if the value did not change, don't call the update callback
			if (sett.get_str(p.first) == p.second) continue;

			sett.set_str(p.first, p.second);
			str_setting_entry_t const& sa = str_settings[index];

			if (sa.fun && callbacks
				&& std::find(callbacks->begin(), callbacks->end(), sa.fun) == callbacks->end())
				callbacks->push_back(sa.fun);
		}

		for (auto const& p : pack->m_ints)
		{
			// disregard setting indices that are not int types
			if ((p.first & settings_pack::type_mask) != settings_pack::int_type_base)
				continue;

			// ignore settings that are out of bounds
			int const index = p.first & settings_pack::index_mask;
			TORRENT_ASSERT_PRECOND(index >= 0 && index < settings_pack::num_int_settings);
			if (index < 0 || index >= settings_pack::num_int_settings)
				continue;

			// if the value did not change, don't call the update callback
			if (sett.get_int(p.first) == p.second) continue;

			sett.set_int(p.first, p.second);
			int_setting_entry_t const& sa = int_settings[index];
			if (sa.fun && callbacks
				&& std::find(callbacks->begin(), callbacks->end(), sa.fun) == callbacks->end())
				callbacks->push_back(sa.fun);
		}

		for (auto const& p : pack->m_bools)
		{
			// disregard setting indices that are not bool types
			if ((p.first & settings_pack::type_mask) != settings_pack::bool_type_base)
				continue;

			// ignore settings that are out of bounds
			int const index = p.first & settings_pack::index_mask;
			TORRENT_ASSERT_PRECOND(index >= 0 && index < settings_pack::num_bool_settings);
			if (index < 0 || index >= settings_pack::num_bool_settings)
				continue;

			// if the value did not change, don't call the update callback
			if (sett.get_bool(p.first) == p.second) continue;

			sett.set_bool(p.first, p.second);
			bool_setting_entry_t const& sa = bool_settings[index];
			if (sa.fun && callbacks
				&& std::find(callbacks->begin(), callbacks->end(), sa.fun) == callbacks->end())
				callbacks->push_back(sa.fun);
		}
	}

	void settings_pack::set_str(int const name, std::string val)
	{
		TORRENT_ASSERT((name & type_mask) == string_type_base);
		if ((name & type_mask) != string_type_base) return;
		std::pair<std::uint16_t, std::string> v(aux::numeric_cast<std::uint16_t>(name), std::move(val));
		insort_replace(m_strings, std::move(v));
	}

	void settings_pack::set_int(int const name, int const val)
	{
		TORRENT_ASSERT((name & type_mask) == int_type_base);
		if ((name & type_mask) != int_type_base) return;
		std::pair<std::uint16_t, int> v(aux::numeric_cast<std::uint16_t>(name), val);
		insort_replace(m_ints, v);
	}

	void settings_pack::set_bool(int const name, bool const val)
	{
		TORRENT_ASSERT((name & type_mask) == bool_type_base);
		if ((name & type_mask) != bool_type_base) return;
		std::pair<std::uint16_t, bool> v(aux::numeric_cast<std::uint16_t>(name), val);
		insort_replace(m_bools, v);
	}

	bool settings_pack::has_val(int const name) const
	{
		switch (name & type_mask)
		{
			case string_type_base:
			{
				// this is an optimization. If the settings pack is complete,
				// i.e. has every key, we don't need to search, it's just a lookup
				if (m_strings.size() == settings_pack::num_string_settings)
					return true;
				std::pair<std::uint16_t, std::string> v(aux::numeric_cast<std::uint16_t>(name), std::string());
				auto i = std::lower_bound(m_strings.begin(), m_strings.end(), v
						, &compare_first<std::string>);
				return i != m_strings.end() && i->first == name;
			}
			case int_type_base:
			{
				// this is an optimization. If the settings pack is complete,
				// i.e. has every key, we don't need to search, it's just a lookup
				if (m_ints.size() == settings_pack::num_int_settings)
					return true;
				std::pair<std::uint16_t, int> v(aux::numeric_cast<std::uint16_t>(name), 0);
				auto i = std::lower_bound(m_ints.begin(), m_ints.end(), v
						, &compare_first<int>);
				return i != m_ints.end() && i->first == name;
			}
			case bool_type_base:
			{
				// this is an optimization. If the settings pack is complete,
				// i.e. has every key, we don't need to search, it's just a lookup
				if (m_bools.size() == settings_pack::num_bool_settings)
					return true;
				std::pair<std::uint16_t, bool> v(aux::numeric_cast<std::uint16_t>(name), false);
				auto i = std::lower_bound(m_bools.begin(), m_bools.end(), v
						, &compare_first<bool>);
				return i != m_bools.end() && i->first == name;
			}
		}
		TORRENT_ASSERT_FAIL();
		return false;
	}

	std::string const& settings_pack::get_str(int name) const
	{
		static std::string const empty;
		TORRENT_ASSERT_PRECOND((name & type_mask) == string_type_base);
		if ((name & type_mask) != string_type_base) return empty;

		// this is an optimization. If the settings pack is complete,
		// i.e. has every key, we don't need to search, it's just a lookup
		if (m_strings.size() == settings_pack::num_string_settings)
		{
			TORRENT_ASSERT(m_strings[name & index_mask].first == name);
			return m_strings[name & index_mask].second;
		}
		std::pair<std::uint16_t, std::string> v(aux::numeric_cast<std::uint16_t>(name), std::string());
		auto i = std::lower_bound(m_strings.begin(), m_strings.end(), v
				, &compare_first<std::string>);
		if (i != m_strings.end() && i->first == name) return i->second;
		return empty;
	}

	int settings_pack::get_int(int name) const
	{
		TORRENT_ASSERT_PRECOND((name & type_mask) == int_type_base);
		if ((name & type_mask) != int_type_base) return 0;

		// this is an optimization. If the settings pack is complete,
		// i.e. has every key, we don't need to search, it's just a lookup
		if (m_ints.size() == settings_pack::num_int_settings)
		{
			TORRENT_ASSERT(m_ints[name & index_mask].first == name);
			return m_ints[name & index_mask].second;
		}
		std::pair<std::uint16_t, int> v(aux::numeric_cast<std::uint16_t>(name), 0);
		auto i = std::lower_bound(m_ints.begin(), m_ints.end(), v
				, &compare_first<int>);
		if (i != m_ints.end() && i->first == name) return i->second;
		return 0;
	}

	bool settings_pack::get_bool(int name) const
	{
		TORRENT_ASSERT_PRECOND((name & type_mask) == bool_type_base);
		if ((name & type_mask) != bool_type_base) return false;

		// this is an optimization. If the settings pack is complete,
		// i.e. has every key, we don't need to search, it's just a lookup
		if (m_bools.size() == settings_pack::num_bool_settings)
		{
			TORRENT_ASSERT(m_bools[name & index_mask].first == name);
			return m_bools[name & index_mask].second;
		}
		std::pair<std::uint16_t, bool> v(aux::numeric_cast<std::uint16_t>(name), false);
		auto i = std::lower_bound(m_bools.begin(), m_bools.end(), v
			, &compare_first<bool>);
		if (i != m_bools.end() && i->first == name) return i->second;
		return false;
	}

	void settings_pack::clear()
	{
		m_strings.clear();
		m_ints.clear();
		m_bools.clear();
	}

	void settings_pack::clear(int const name)
	{
		switch (name & type_mask)
		{
			case string_type_base:
			{
				std::pair<std::uint16_t, std::string> v(aux::numeric_cast<std::uint16_t>(name), std::string());
				auto const i = std::lower_bound(m_strings.begin(), m_strings.end()
					, v, &compare_first<std::string>);
				if (i != m_strings.end() && i->first == name) m_strings.erase(i);
				break;
			}
			case int_type_base:
			{
				std::pair<std::uint16_t, int> v(aux::numeric_cast<std::uint16_t>(name), 0);
				auto const i = std::lower_bound(m_ints.begin(), m_ints.end()
					, v, &compare_first<int>);
				if (i != m_ints.end() && i->first == name) m_ints.erase(i);
				break;
			}
			case bool_type_base:
			{
				std::pair<std::uint16_t, bool> v(aux::numeric_cast<std::uint16_t>(name), false);
				auto const i = std::lower_bound(m_bools.begin(), m_bools.end()
					, v, &compare_first<bool>);
				if (i != m_bools.end() && i->first == name) m_bools.erase(i);
				break;
			}
		}
	}
}
